1. Field of the Invention
The invention concerns variable-thickness molded composite panels comprising a base layer of bound fibers and a cover sheet, particularly acoustical panels having at least one thick portion for absorbing sounds and other thinner, rigid portions, notably the edges, that serve particularly for mounting the panels. More specifically, the invention concerns a process and means for producing such panels.
Examples of composite panels of this type are stationary, removable, or movable baffles or screens that may be hung from the ceiling, formed into walls, etc., or made into hood-liners or interior fittings for the roofs of motor vehicles.
2. Description of the Prior Art
Composite acoustical panels are made by molding a piece of raw material, i.e., a bed or layer of fibers impregnated with a nonpolymerized binder (generally a thermosetting resin). The raw material is covered on at least one side by a cover sheet lending the desired characteristics to the finished product, e.g., an aesthetic appearance. Said cover sheet is bound to the layer of fibers in a one-step press-molding operation that takes place simultaneously with the polymerization of the binder.
One of the problems encountered in the one-step molding of composite panels of the type described above stems from the difficulty of obtaining rapid, complete, and uniform polymerization in the thick, absorbent portion of low fiber-density as well as in the other parts (notably the thin edges) that are of high fiber-density.
In conventional press-molding, the composite is heated by conduction resulting from contact with the heated mold and mold-backing, which requires a long molding period for the thick section, a period which is not necessary for, and even harmful to, the thinner edges. To overcome this problem it has already been proposed to blow hot air through the pad during molding so that the heat necessary for polymerization is brought quickly into the center of the pad and the length of the operation is thereby reduced.
Another problem encountered in the molding of variable-thickness composite panels lies in obtaining the correct conformation of panel to mold, particularly when the latter contains sharp angles and/or curves and large variations in thickness.
To date, known molding processes do not make it possible to produce composite panels (and particularly acoustical panels) having simultaneously a good appearance and a shape that is consistent from one panel to the next (particularly for highly curved shapes and where the absorbent section is very thick) while at the same time retaining a minimal pressing time compatible with industrial production, e.g., two minutes, thirty seconds or less.
The invention disclosed and claimed herein, overcomes these drawbacks and offers a process for the industrial production of such composite panels.